Conventionally, sensors utilizing the phenomenon in which the surface plasmon resonance decreases the intensity of reflected light having a specific wavelength have been proposed for use in analysis of biomolecules and the like, and for example, a surface plasmon sensor having as essential constituents a prismatic dielectric block and a metal film which is formed on the dielectric block and is to be arranged in contact with a specimen has been disclosed in, for example, Japanese Unexamined Patent Publication No. 6 (1994)-167443. In such a surface plasmon sensor, a total reflection condition is satisfied at the interface between the dielectric block and the metal film. It is possible to perform measurement of the refractive index or concentration of a specimen, identification of the specimen, and the like by applying light for measurement to the surface plasmon sensor so that surface plasmon resonance causes attenuated total reflection, measuring the intensity of light totally reflected at the interface, and detecting the attenuated total reflection.
However, since the above surface plasmon sensor uses the prismatic dielectric block, the cost of the surface plasmon sensor is high, and the surface plasmon sensor has severe structural constraints on downsizing or adaptation to concurrent analysis of a number of specimens. In order to solve this problem, a sensor which utilizes a phenomenon in which localized plasmon resonance attenuates the intensity of reflected light at a specific wavelength has been proposed, and a local plasmon sensor in which a metal structure is formed with fine protrusions and recesses at a surface of a substrate so that localized plasmon resonance is effectively excited has also been proposed. See Japanese Unexamined Patent Publication No. 2004-232027, and T. Okamoto et al., “Local plasmon sensor with gold colloid monolayers deposited upon glass substrates,” Optics Letters, Vol. 25, Issue 6, pp. 372-374 (2000).
Since the above local plasmon sensor does not need the prismatic dielectric block, the local plasmon sensor can be more simply constructed at lower cost than the surface plasmon sensor, and the local plasmon sensor has weaker structural constraints than the surface plasmon sensor. However, the detection sensitivity of the local plasmon sensor is poor compared with the surface plasmon sensor, so that it is difficult to perform high-precision analysis by using the local plasmon sensor.